1. Technical Field
The present invention relates generally to position sensors, and, more particularly, to a non-contact linear absolute position sensor.
2. Description of the Related Art
Angular and linear position sensors are widely used in automatic control systems as feedback-sensing devices in one or more control loops of the system. In the automotive industry, such position information may be used in substitution of more traditional, conventional control feedback provided by mechanical linkages, such as cables, rods, and the like.
For example, in the automotive field, it may be desirable to know the linear absolute position of a long travel mechanism, such as a rack and pinion mechanism (i.e., that moves when a driver of an automotive vehicle turns the steering wheel), or the position of a sliding door on a minivan. In the first example, a linear absolute position sensor can provide information as to the absolute linear position of the rack and pinion mechanism, which corresponds to the orientation of the front wheels (i.e., the steering wheels) of the automotive vehicle. In the second example, it may be desirable to know exactly where the sliding door is positioned within the long travel between a completely closed position and a completely open position. There are many other examples in and outside of the automotive industry. Non-contact linear absolute position sensing has conventionally been accomplished using a variety of technologies including inductive, optical, capacitive, and Hall Effect (i.e., magnetic flux intensity).
For example, inductive sensors are mechanically sturdy, but can be influenced by stray or externally-generated electromagnetic fields. Optical-based sensors are generally very accurate but require a relatively high degree of tolerancing on the parts, and are subject to strict sealing requirements in order to prevent or minimize dust from entering into the assembly, which can adversely influence an otherwise accurate measurement. Capacitive-based sensing technology generally provides satisfactory results but for conventional sized sensors the capacitance is generally relatively small and accordingly humidity and/or electromagnetic fields can also greatly influence an otherwise accurate measurement.
It is also known to use Hall Effect sensing technology for measuring absolute linear position, but such conventional approaches generally require very good material properties on the magnet and require flux concentrators made of a low hysteresis material. Additionally, these concentrators often require very accurate dimensioning and positioning. It is also very hard to achieve good temperature compensation using Hall Effect sensors alone. This problem is increased when you have to compensate for a component's position variation due to temperature.
U.S. Patent Application Publication No. 2004/0164727 A1 entitled “SINGLE MAGNET LINEAR POSITION SENSOR” discloses a sensor assembly for measuring linear position that includes a ferromagnetic flux concentrator, a magnet, and a galvanomagnetic sensing element such as a Hall Effect or magnetoresistive sensor.
In view of the foregoing, there is a need to provide a non-contact linear absolute position sensor that minimizes or eliminates one or more of the shortcomings referred to above.